Method and device for simulating a radio channel

ABSTRACT

The invention relates to a device and a method for simulating a radio channel, wherein a signal transmitted and received by more than one antenna is simulated. The method comprises supplying an input signal of each antenna to a similar delay line, each delay line comprising a delay element connected in series for each propagation path, weighting an output signal of the delay elements corresponding with each propagation path by a term in dependence of a control vector of each transmitting antenna, by a term describing the distortion of a propagation path, and by a term in dependence of a control vector of each receiving antenna, and adding up the components corresponding with each receiving antenna and obtained from the outputs of the weighting means.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase application of InternationalApplication No. PCT/FI02/00869 filed Nov. 7, 2002, which is incorporatedherein by reference.

FIELD OF THE INVENTION

The invention relates to a method and a device implementing the methodfor simulating a radio channel. The invention particularly relates to asituation wherein several antennas are used in transmitting and/orreceiving a signal propagating through a radio channel.

BRIEF DESCRIPTION OF THE RELATED ART

An essential problem with radio systems is the fast variation of radiochannel properties as a function of time. This relates to mobiletelephone systems in particular wherein at least one of the parties to aconnection is often a mobile one. The attenuation and impulse responseof a radio channel then vary within a large phase and amplitude areaeven thousands of times per second. The phenomenon is random in nature,so mathematically it can be described statistically. The phenomenonmakes radio connections and devices to be used more difficult to design.

Several reasons exist for radio channel variation. When aradio-frequency signal is transmitted from a transmitter to a receiverin a radio channel, the signal propagates via one or more paths, thephase and amplitude of the signal varying on each propagation path.Phase variation in particular causes fades of different duration andstrength to the signal. Noise and interference caused by othertransmitters also interfere with a radio connection.

A radio channel can be tested either under real conditions or by using asimulator simulating real conditions. Tests conducted under realconditions are difficult since tests conducted e.g. outdoors areaffected e.g. by the weather and the seasons, which change all the time.Measurements conducted even at the same location give different resultsat different times. Furthermore, a test conducted in one environment(city A) does not completely apply to a similar environment (city B).The worst possible situation cannot often be tested under realconditions, either.

A device simulating a radio channel, on the other hand, can be used forquite freely simulating a radio channel having desired features betweentwo radio devices such that the radio devices operate at their naturaltransmission rates, as in a real operating situation.

Typically between a transmitter and a receiver, several propagationpaths exist via which a signal propagates and, furthermore, if severaltransmitting and/or receiving antennas are used, the situation becomessubstantially heavier to simulate. Assume, for instance, an arrangementwhich includes M transmitting antennas, a radio channel and N receivingantennas. In such a case, the channel is a Multiple Input MultipleOutput (MIMO) radio channel, which is described by an N×M transfermatrix. Each (n,m) element in the matrix is a time-varying impulseresponse for a sequence comprising the m^(th) transmitting antenna, then^(th) receiving antenna and the radio channel.

In prior art solutions, in order to simulate the shown situation, eachmatrix element is simulated by a time-varying, transversal filter,typically by an FIR filter. The total number of FIR filters needed isthus M×N. An arrangement is further needed to describe the correlationbetween the different elements of the matrix. If it is assumed that thenumber of different propagation paths of the signals is K, thecomplexity of the implementation of the prior art calculation method,expressed as the necessary multiplications, delay elements andadditions, is M×N×K delays, M×N×K multiplications and M×N×K additions.It is to be noted that the complexity of a K input adder is K. Theeffect of the calculation of the correlation between the elements of thetransfer matrix has not been taken into account herein.

When the number of transmitting and receiving antennas increases, thecomplexity required by the calculation increases dramatically. Thesimulation of MIMO systems has thus required an extremely heavycalculation capacity. This is a difficult problem since due to theirpotential advantages, this type of systems have become increasinglyattractive.

SUMMARY OF THE INVENTION

An object of the invention is to provide a method and an apparatusimplementing the method such that simulation of a MIMO radio channelbecomes easy to implement. This is achieved by a method for simulating aradio channel, wherein a signal transmitted by more than one antenna andreceived by one or more antennas as well as propagated via one or morepropagation paths is simulated. The method of the invention comprisessupplying an input signal of each transmitting antenna to a similardelay line, each delay line comprising a delay element connected inseries for each propagation path, weighting, in weighting means, anoutput signal of the delay elements corresponding with each propagationpath by a term in dependence of a control vector of each transmittingantenna, by a term describing the distortion of a propagation path, andby a term in dependence of a control vector of each receiving antenna, asignal component thus being provided for each receiving antenna, andadding up the components corresponding with each receiving antenna andobtained from the outputs of the weighting means.

The invention also relates to a device for simulating a radio channel,wherein a signal transmitted by more (M) than one antenna and receivedby one or more antennas (N) as well as propagated via one or morepropagation paths is simulated. The device of the invention comprises Msimilar delay lines, each delay line comprising a delay elementconnected in series for each propagation path, the input of the delaylines comprising M signals to be transmitted, a number of weightingmeans whose input comprises output signals of the delay elementscorresponding with each propagation path, the output signals beingweighted by a term describing the distortion of a correspondingpropagation path, by a term in dependence of a control vector of eachtransmitting antenna and by a term in dependence of a control vector ofeach receiving antenna, the terms being located in other inputs, andwhose output comprises a signal for each receiving antenna, and an adderconfigured to add up the terms corresponding with each receiving antennaand obtained from the outputs of the weighting means.

A solution of the invention may be implemented both as a hardware- and asoftware-based implementation. A simulator according to the preferredembodiments is implemented by means of delay lines, weighting means andan adder. The number of delay lines is preferably the same as the numberof transmitting antennas. The elements of the delay lines correspondwith the numbers of propagation paths. Signals propagated through eachpropagation path are weighted by a term describing the distortion of thepropagation path and terms in dependence of the control vectors of thetransmitting and receiving antennas. Finally, the terms correspondingwith each receiving antenna are added up.

The method and device of the invention provide several advantages. Thesolution disclosed enables the amount of calculation needed in thesimulation of a radio channel to be reduced substantially. Thecalculation of the correlation between different transfer matrixelements also becomes smoothly taken into account during thecalculation. If it is assumed that the number of transmitting antennasis M, the number of receiving antennas is N and the number of differentpropagation paths of the signals is K, the complexity in the solutionsaccording to the preferred embodiments is M×K delays, (M+N+1)×Kmultiplications and (N+1)×K additions. Compared to the previoussolutions, the complexity reduction factor is thus at least N fordelays, (M×N)/(M+N+1) for the number of multiplications and (M×N)/(N+1)for the number of additions. Consequently, the simulating apparatus ofthe disclosed solution is substantially more advantageous and easier toimplement than the previous solutions that have required a heaviercalculation capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in closer detail in connection with thepreferred embodiments and with reference to the accompanying drawings,in which

FIG. 1A illustrates a signal propagation environment typical of radiosystems,

FIG. 1B clarifies the designations used,

FIG. 2 shows an example wherein a radio channel is static,

FIGS. 3A and 3B illustrate examples of implementation of a calculationelement,

FIG. 4 shows an example wherein a radio channel varies according to timeand frequency,

FIGS. 5A to 5D illustrate examples of implementation of a simulatingapparatus,

FIG. 6 illustrates an example of a preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, let us define some terms. Examine an example according to FIG. 1Aof a signal propagation environment typical of radio systems. The figureshows a transmitting antenna 100 and a receiving antenna 102, and anumber of propagation paths 104, 106 for signal waves therebetween. Letthe number of propagation paths be K. A wave encounters a number ofobstructions on a propagation path. Upon encountering an obstruction,the wave may e.g. be reflected, or it may scatter or spread. In eachencounter, the amplitude of the wave is attenuated and its phasechanges, depending on the characteristics of the obstacle and the inputand output angles of the wave.

When the transmitting antenna 100 is moved slightly, typically for somemultiples of the wavelength of a signal to be transmitted, the geometryof the propagation path of the signal waves remains substantially thesame. An area within which the transmitting antenna can be moved withoutthe geometry of the propagation path changing is shown by R₁ in FIG. 1.Similarly, R₂ designates an area within which the receiving antenna 102can be moved without the geometry of the propagation path of the signalwaves substantially changing. Let us use a coordinate system whereinorigins O₁ and O₂, correspondingly, have been determined to a randompoint within area R₁ and area R₂, respectively. The locations of theantennas 100 and 102 thus completely determine vectors r₁ ∈ R³ and r₂ ∈R³, wherein R is a real axis.

Let x ∈ C (wherein C is a complex space) a complex envelope signal inthe input of a transmitting antenna when the antenna is located at r₁ ∈R₁. Now, the component caused by the k^(th) wave in the output of areceiving antenna located at r₂ ∈ R₂ can be described by the formula:y _(k)(r ₁ ,r ₂)=α_(k) exp{j2πλ₀ ⁻¹(Ω_(1k) ·r ₁)}exp{j2πλ₀ ⁻¹(Ω_(2k) ·r₂)}x.

Here λ₀ is the wavelength of the signal and (·) refers to a scalarproduct. Furthermore, α_(k) is a complex attenuation coefficient of thek^(th) wave, and Ω_(1k) as well as Ω_(2k) refer to the output and inputangles of the wave with respect to the transmitting and receivingantennas. The designations of the formula will be clarified in FIG. 1Bwhich shows origin O₁ while r_(h), r_(v) and r_(z) designate axes. Thefigure shows circle S₂ whose radius is one and wherein point Ω islocated. The direction of the wave can be determined as a unit vectorterminating at point Ω. Point Ω is unambiguously determined by itsspherical coordinates (φ,θ)∈[−π,π)×[−π,π] according to the followingrelation:Ω=e(φ,θ)≐[cos(φ)sin(θ), sin(φ)sin(θ), cos(θ)]^(T).

Here ( )^(T) is a transposition operation. Angles φ and θ are called theazimuth angle and the coelevation angle of Ω. The complex attenuationcoefficient α_(k) depends on the interactions between the k^(th) waveand the obstructions on the propagation path, the length of thepropagation path of the wave as well as on the characteristics of thefield patterns of the transmitting and receiving antennas in directionsΩ_(1k) and Ω_(2k).

Next, let us examine the situation shown in FIG. 2 wherein Mtransmitting antennas 200 and N receiving antennas 202 are positioned inareas R₁ and R₂. If x_(m) describes the signal in the input of them^(th) transmitting antenna located at r_(1,m) ∈ R₁, m=1, . . . ,M, anoutput signal of the n^(th) receiving antenna at r_(2,n) ∈ R₂ can bedescribed by the formula

${y_{n} = {\sum\limits_{m = 1}^{M}{{H\left( {r_{1,m},r_{2,n}} \right)}x_{m}}}},\mspace{14mu}{n = 1},\ldots\mspace{14mu},{N.}$

The above N linear equations can be described in a matrix form in thefollowing manner:

$\begin{matrix}{\begin{bmatrix}y_{1} \\\vdots \\y_{N}\end{bmatrix} = {\begin{bmatrix}H_{1,1} & \ldots & H_{1,M} \\\vdots & \; & \vdots \\H_{N,1} & \ldots & H_{N,M}\end{bmatrix}\begin{bmatrix}x_{1} \\\vdots \\x_{M}\end{bmatrix}}} & (1)\end{matrix}$wherein designation H_(n,m)≐H(r_(1,m), r_(2,n)) is used.

When the locations of the transmitting and receiving antennas are takeninto account, the above designation can be expressed in the formH _(n,m)=∫∫exp{j2πλ₀ ⁻¹(Ω₁ ·r _(1,m))}exp{j2πλ₀ ⁻¹(Ω₂ ·r_(2,n))}h(Ω₁,Ω₂)dΩ ₁ dΩ ₂.  (2)

Here, the term h(Ω₁,Ω₂) can be called a bidirectional input angle spreadfunction. In this case, it is a discrete function of the form

$\begin{matrix}{{h\left( {\Omega_{1},\Omega_{2}} \right)} = {\sum\limits_{k = 1}^{K}{\alpha_{k}{\delta\left( {\Omega_{1} - \Omega_{1k}} \right)}{\delta\left( {\Omega_{2} - \Omega_{2k}} \right)}}}} & (3)\end{matrix}$It describes spreading in the propagation direction of the signaljointly within areas R₁ and R₂. In a general case, it does not have tobe a discrete function but if it is of the form of Formula (3), theportion of one wave in h(Ω₁,Ω₂) is a Dirac impulse weighted by α_(k) andlocalised to point (Ω_(1k),Ω_(2k)) in space S₂×S₂≐(S₂)².

Equation (1) can be expressed in a compact form asy=Hx,  (4)wherein x on M dimensional complex value vector x ≐ [x₁, . . .,x_(M)]^(T), y is N dimensional complex value vector y ≐ [y₁, . . .,y_(M)]^(T), and H is N×M dimensional complex value matrix H ≐[H_(n,m)]_(n∈{1, . . . ,N}, m∈{1, . . . ,M}).

Formula (4) thus determines the input and output relation for a MIMOchannel comprising M transmitting antennas, a radio wave propagationpath and N receiving antennas. Matrix H is called the transfer matrix ofthe channel. Its coefficients depend on the structure of the antennaarrays used in transmission and reception as well as on the conditionsof the radio channel.

Examine the structure of matrix H in closer detail, particularlyfocusing on the exponent terms of Formula (2). The M and N dimensionalvectorsc ₁(Ω₁)≐[exp{j2πλ₀ ⁻¹(Ω₁ ·r _(1,1))}, . . . , exp{j2πλ₀ ⁻¹(Ω₁ ·r_(1,M))}]^(T)  (5)c ₂(Ω₂)≐[exp{j2πλ₀ ⁻¹(Ω₂ ·r _(2,1))}, . . . , exp{j2πλ₀ ⁻¹(Ω₂ ·r_(2,N))}]^(T)  (6)

-   -   present a response of two antenna arrays to a wave being        received/transmitted at a certain angle Ω₁ and Ω₂ with respect        to the antenna arrays. These vectors can be called antenna        control vectors. They describe how signals received by different        antenna elements differ from each other, e.g. for the phase.        Using these vectors, Formula (2) can be expressed in the form        H _(n,m) =∫∫[c ₁(Ω₁)]_(m) [c ₂(Ω₂)]_(n) h(Ω₁,Ω₂)dΩ ₁ dΩ ₂.  (7)

The transfer matrix thus being of the formH=∫∫c ₂(Ω₂)c ₁(Ω₁)^(T) h(Ω₁,Ω₂)dΩ ₁ dΩ ₂.  (8)

In a discrete case, wherein the bidirectional input angle spreadfunction is of form (3), Formula (8) is reduced to a sum

$\begin{matrix}{H = {\sum\limits_{k = 1}^{K}{\alpha_{k}c_{2,k}c_{1,k}^{T}}}} & (9)\end{matrix}$whereinc _(1,k) ≐c ₁(Ω_(1k))[exp{j2πλ₀ ⁻¹(Ω_(1k) ·r _(1,1))}, . . . , exp{j2πλ₀⁻¹(Ω_(1k) ·r _(1,M))}]^(T).c _(2,k) ≐c ₂(Ω_(2k))[exp{j2πλ₀ ⁻¹(Ω_(2k) ·r _(2,1))}, . . . , exp{j2πλ₀⁻¹(Ω_(2k) ·r _(2,N))}]^(T) .

In the discrete case, the effect of one wave on the transfer matrix isthus a unit rank matrix. As the received signal, Formulas (2) and (9)now give

$\begin{matrix}{y = {\sum\limits_{k = 1}^{K}{\alpha_{k}c_{2,k}c_{1,k}^{T}{x.}}}} & (10)\end{matrix}$

-   -   and for one sum term y_(k),        y _(k) ≐c _(2,k)α_(k) c _(1,k) ^(T) x  (11)    -   is thus valid.

FIGS. 3A and 3B illustrate the implementation of this calculation in asimulating apparatus in accordance with the preferred embodiments. InFIG. 3A, an input comprises signal components 300 x_(m), m=1, . . . ,Mtransmitted from each antenna. Each of these is supplied to a multiplier302, 304, in which the signal components are multiplied by element[c_(1,k)]_(m) of a control vector of each transmitting antenna. Thesecomponents multiplied by the control vector are added up in an adder306, and the sum signal obtained is multiplied in a multiplier 308 bycomplex attenuation coefficient α_(k). The sum signal thus obtained issupplied to a number N of multipliers 310, 312, wherein N is thus thenumber of receiving antennas. In the multipliers 310, 312, each signalcomponent is multiplied by element [c_(2,k)]_(n) of a control vector ofa corresponding receiving antenna. Output signals y_(k,n) of thereceiving antennas are obtained from an output 314 of the multipliers.FIG. 3B illustrates an equivalent implementation of the solution. Thesolution may be implemented either by software or hardware. The signalcomponents 300 transmitted from each antenna, antenna control vectorsc_(1,k) and c_(2,k,) and complex attenuation coefficient α_(k) areneeded as inputs while the output signals y_(k) 314 of the receivingantennas are needed as an output. The structure described herein enablesparticularly the correlations between the different elements of thetransfer matrix to be taken into account for each wave.

A situation has been examined above wherein no channel variation withrespect to time and frequency has been taken into account. FIG. 4illustrates a situation wherein a radio channel varies according to timeand frequency. Time variation is caused e.g. by a movement of an antennaor a reflective surface. Such a situation is modeled herein by assumingthat a propagated wave has a certain constant Doppler frequency. Let usdesignate the Doppler frequency of wave k by term ν_(k). Frequencyvariation is caused by alteration in the lengths of the propagationpaths of waves. Let us designate the proportional delay of wave k byterm τ_(k).

Here, too, let us use a coordinate system wherein origins O₁ and O₂,correspondingly, have been determined to a random point within area R₁and area R₂, respectively. The figure shows M transmitting antennas 400,whose input comprises a signal x(t) 402, as a function of time, to betransmitted. Vectors r_(1,1), . . . , r_(1,M) describe the location ofthe antennas with respect to the arbitrarily selected origin O₁.Correspondingly, the location of N receiving antennas 404 with respectto origin O₂ is described by vectors r_(2,1), . . . , r_(2,N).

Now, the signal component y_(nm)(t) generated by x_(m)(t) and located inthe output of the n^(th) receiving antenna is

$\begin{matrix}{{y_{nm}(t)} = {\int{{h\left( {r_{1,m},r_{2,n},{t;\tau}} \right)}{x_{m}\left( {t - \tau} \right)}{\mathbb{d}\tau}}}} \\{= {\int{{h_{n,m}\left( {t;\tau} \right)}{x_{m}\left( {t - \tau} \right)}{\mathbb{d}\tau}}}}\end{matrix}$whereinh _(n,m)(t;τ)≐h(r _(1,m) ,r _(2,n) ,t;τ).  (12)

The signal in the output of the n^(th) receiving antenna is

$\begin{matrix}{{y_{n}(t)} = {\sum\limits_{m = 1}^{M}{y_{nm}(t)}}} \\{{= {\sum\limits_{m = 1}^{M}{\int{{h_{n,m}\left( {t;\tau} \right)}{x_{m}\left( {t - \tau} \right)}{\mathbb{d}\tau}}}}},{n = 1},\ldots\mspace{14mu},{N.}}\end{matrix}$Arranging n above equations in a matrix form yields the followingformulay(t)=∫h(t;τ)×(t−τ)dτ,  (13)whereinx(t)≐[x ₁(t), . . . , x _(M)(t)]^(T)y(t)≐[y ₁(t), . . . , y _(N)(t)]^(T)h(t;τ)≐[h _(n,m)(t;τ)]_(n∈{1, . . . ,N}, m∈{1, . . . ,M}).  (14)

The term h(t; τ) can be called a time-depending broadband transfermatrix or a time-depending impulse response in a MIMO radio channel.

A time-depending channel matrix can be described in closer detail ifFormulas (5) and (6) are taken into account. Utilizing the two formulas,Formula (14) can be written as follows:

$\begin{matrix}{{h\left( {t;\tau} \right)} = {\int{\int{\int{\exp\left\{ {j\; 2{{\pi\lambda}_{0}^{- 1}\left( {\Omega_{1} \cdot r_{1,m}} \right)}\exp{\left\{ {j\; 2\;{{\pi\lambda}_{0}^{- 1}\left( {\Omega_{2} \cdot r_{2,n}} \right)}} \right\} \cdot}} \right.}}}}} \\{{\exp\left\{ {j\; 2\;\pi\; v} \right\}{h\left( {\Omega_{1},\Omega_{2},v,\tau} \right)}{\mathbb{d}\Omega_{1}}{\mathbb{d}\Omega_{2}}{{\mathbb{d}v}.}}\;} \\{= {\int{\int{\int{{\left\lbrack {c_{1}\left( \Omega_{1} \right)} \right\rbrack_{m}\left\lbrack {c_{2}\left( \Omega_{2} \right)} \right\rbrack}_{n}\exp\left\{ {{j2}\;\pi\; v} \right\}{h\left( {\Omega_{1},\Omega_{2},v,\tau} \right)}}}}}} \\{{\mathbb{d}\Omega_{1}}{\mathbb{d}\Omega_{2}}{{\mathbb{d}v}.}}\end{matrix}$

It can be inferred from this that h(t; τ) can be expressed in the formh(t;τ)=∫∫∫c ₂(Ω₂)c ₁(Ω₁)^(T) exp{j2πν}h(Ω₁,Ω₂,ν,τ)dΩ ₁ dΩ ₂ dν  (15)

Now, by inserting the right-hand side of this formula into Formula (13)and by arranging the terms, a relation is achieved for the radio channelvarying with respect to time and frequency, the relation beingy(t)=∫∫∫∫c ₂(Ω₂)c ₁(Ω₁)^(T)×(t−τ)exp{j2πν}h(Ω₁,Ω₂,ν,τ)dΩ ₁ dΩ ₂dνdτ.  (16)

In the discrete case, equations (15) and (16) are reduced to be of theform

$\begin{matrix}{{h\left( {t;\tau} \right)} = {\sum\limits_{k = 1}^{K}{\alpha_{k}\exp\left\{ {j\; 2\;\pi\; v_{k}t} \right\} c_{2,k}c_{1,k}^{T}{\delta\left( {\tau - \tau_{k}} \right)}}}} & (17) \\{{y(t)} = {\sum\limits_{k = 1}^{K}{\alpha_{k}\exp\left\{ {j\; 2\;\pi\; v_{k}t} \right\} c_{2,k}c_{1,k}^{T}{{x\left( {\tau - \tau_{k}} \right)}.}}}} & (18)\end{matrix}$

FIG. 5A illustrates examples of an arrangement for implementing thesimulation in accordance with a preferred embodiment the invention. Thearrangement comprises a simulator 500, in which the necessarycalculation operations for implementing the simulation can beimplemented as solutions based either on hardware or software. In theexample of the figure, M signals 502 x₁(t), . . . , x_(M)(t) aresupplied to the simulator as input, the signals thus corresponding witha signal component to be supplied to M transmitting antennas.Correspondingly, N signals 504 y₁(t), . . . , y_(N)(t) are obtained asoutput, the signals thus corresponding with the signal component to beobtained from N receiving antennas. The control of the simulator, suchas feeding of simulating parameters and the user interface, is carriedout from a control unit 506.

FIG. 5B illustrates another example otherwise similar to the previousone except that the input signal 502 is one signal x(t) which, whennecessary, is divided to two or more branches inside the simulator. Insuch a case, each transmitting antenna thus transmits the same signalcomponent.

FIG. 5C illustrates still another example wherein the output signal 504has been combined into one signal y(t). In all the examples above, theinput and output signals 502, 504 of the simulating apparatus 500 may beeither radio frequency or baseband frequency ones, either analog ordigital. Furthermore, no separate control unit 506 is necessarily neededbut the control unit may be integrated into the simulating apparatus.The simulating apparatus may also comprise both an integrated and anexternal control unit which can be e.g. a computer connected to thesimulating apparatus by a suitable bus interface.

FIG. 5D illustrates further different input/output alternatives. Theinput comprises an analog radio frequency signal 508, which is convertedin a converter 510 into a baseband analog signal. This signal issupplied to an A/D converter 512, in which it is converted into adigital form, i.e. a digital baseband signal is obtained. This issupplied to the simulating unit 500, whose output further comprises adigital baseband output signal. This is forwarded to a D/A converter 514whose output comprises an analog baseband signal. In a converter 516,this is converted into a radio frequency analog signal. Implementing theinputs and outputs in different stages of the above-describedarrangement enables simulating solutions of different types to beimplemented in a versatile manner by using a single simulatingapparatus.

FIG. 6 illustrates an implementation example of a simulator inaccordance with a preferred embodiment of the invention for a discretemodel of a MIMO radio channel. This implementation is in accordance withFormula (18).

M signals x₁(t), . . . , x_(M)(t), which thus correspond with the signalcomponent to be supplied to M transmitting antennas, constitute theinput 502. These signals are supplied to M similar delay lines 600A,600B, each comprising a delay element 602A to 606A, 602B to 604Bconnected in series for each propagation path. The delay elements 602A,602B, wherein delay τ₁ is caused to the signal, i.e. the outputs of thedelay elements comprise signals x₁(t−τ₁), . . . , x_(M)(t−τ₁), thuscorrespond with the first propagation path. The delay elements 604A,604B, wherein delay τ₂−τ₁ is caused to the signal, correspond with thesecond propagation path. The outputs of the delay elements thus comprisesignals x₁(t−τ₂), . . . , x_(M)(t−τ₂). Correspondingly, the delayelements 606A, 606B, wherein delay τ_(K)−τ_(K−1) is caused to thesignal, correspond with the K^(th) propagation path. The outputs of thedelay elements thus comprise signals x₁(t−τ_(K)), . . . ,x_(M)(t−τ_(K)).

The output signals of the delay elements corresponding with eachpropagation path are supplied to weighting means, in which the signal ismultiplied by term α_(k) describing the distortion of a propagationpath, by term c_(1,k) in dependence of a control vector of eachtransmitting antenna and by term c_(2,k) in dependence of a controlvector of each receiving antenna.

The output signals x₁(t−τ₁), . . . , x_(M)(t−τ₁) of the delay elements602A, 602B corresponding with the first propagation path are thussupplied to a weighting means 608, which also receives as input term α₁describing the distortion of the propagation path, as well as antennacontrol vectors c_(1,1) and c_(2,1). These are multiplied with eachother. The output signals x₁(t−τ₂) . . . , x_(M)(t−τ₂) of the delayelements 604A, 604B corresponding with the second propagation path aresupplied to a weighting means 610, which also receives as input term α₂describing the distortion of the second propagation path, as well asantenna control vectors c_(1,2) and c_(2,2). Correspondingly, the outputsignals x₁(t−τ_(K)), . . . , x_(M)(t−τ_(K)) of the delay elements 606A,606B corresponding with the K^(th) propagation path are supplied to aweighting means 612, which also receives as input term α_(K) describingthe distortion of the K^(th) propagation path, as well as antennacontrol vectors c_(1,K) ja c_(2,K).

A preferred embodiment of the weighting means 608 to 612 has beendescribed above in connection with FIGS. 3A and 3B.

The output of each weighting means 608 to 612 comprises a signal foreach receiving antenna. These terms corresponding with each receivingantenna and obtained from the outputs of the weighting means are addedup in adders 614 to 618. The terms corresponding with the firstreceiving antenna are thus added in the adder 614, which yields termy₁(t) and, correspondingly, the terms corresponding with the N^(th)receiving antenna are added up in the adder 618, which yields termy_(N)(t). This results in N signals 504 y₁(t), . . . , y_(N)(t), whichthus correspond with the signal component to be obtained from the N^(th)receiving antenna.

Inputs of the weighting means other than signal terms x_(m)(t), i.e.terms α_(k) describing the distortion of the propagation path, and termsc_(1,k) and c_(2,k) in dependence of the control vector of eachtransmitting and receiving antenna, are obtained either directly fromthe control means 506 of the simulator (FIGS. 5A to 5C), or the controlmeans provide parameters for the calculation thereof.

Although the invention has been described above with reference to theexample in accordance with the accompanying drawings, it is obvious thatthe invention is not restricted thereto but can be modified in many wayswithin the inventive idea disclosed in the attached claims.

1. A method for simulating a radio channel, wherein a signal transmittedby more than one antenna and received by one or more antennas as well aspropagated via one or more propagation paths is simulated, the methodcomprising: supplying an input signal of each transmitting antenna to asimilar delay line, each delay line comprising a delay element connectedin series for each propagation path; weighting, in weighting means, anoutput signal of the delay elements corresponding with each propagationpath by a term in dependence of a control vector of each transmittingantenna, by a term describing the distortion of a propagation path, andby a term in dependence of a control vector of each receiving antenna, asignal component thus being provided for each receiving antenna; andadding up the components corresponding with each receiving antenna andobtained from the outputs of the weighting means.
 2. A method as claimedin claim 1, further comprising: adding up the input signals of theantennas weighted by the control vector of the transmitting antennaprior to weighting by the term describing the distortion of thepropagation path.
 3. A method as claimed in claim 1, further comprising:dividing the signal weighted by the term describing the distortion ofthe propagation path to a branch corresponding with the number ofreceiving antennas.
 4. A method as claimed in claim 1, furthercomprising: selecting the distance between the transmitting antennassuch that the output angles of the signals transmitted from the antennasare equal in size.
 5. A method as claimed in claim 1, furthercomprising: multiplying the output signal of the delay elementscorresponding with each propagation path in a multiplier by the term independence of the control vector of each transmitting antenna, by theterm describing the distortion of a propagation path and by the term independence of the control vector of each receiving antenna.
 6. A devicefor simulating a radio channel, wherein a signal transmitted by morethan one antenna and received by one or more antennas as well aspropagated via one or more propagation paths is simulated, the devicecomprising: M similar delay lines, each delay line comprising a delayelement connected in series for each propagation path, the input of thedelay lines comprising M signals to be transmitted; a number ofweighting means whose input comprises output signals of the delayelements corresponding with each propagation path, the output signalsbeing weighted by a term describing the distortion of a correspondingpropagation path, by a term in dependence of a control vector of eachtransmitting antenna and by a term in dependence of a control vector ofeach receiving antenna, the terms being located in other inputs, andwhose output comprises a signal for each receiving antenna; and an adderconfigured to add up the terms corresponding with each receiving antennaand obtained from the outputs of the weighting means.
 7. A device asclaimed in claim 6, wherein the weighting means are implemented by amultiplier.
 8. A device as claimed in claim 6, wherein the weightingmeans are configured to add up the input signals of the antennasweighted by the control vector of the transmitting antenna prior toweighting by the term describing the distortion of the propagation path.9. A device as claimed in claim 6, wherein the weighting means areconfigured to divide the signal weighted by the term describing thedistortion of the propagation path to a branch corresponding with thenumber of receiving antennas.
 10. A device as claimed in claim 9,wherein the weighting means are configured to weigh each branch by theterm in dependence of the control vector of a corresponding receivingantenna.